1. Field of the Invention
This invention relates to the isolation of a novel beta integrin subunit polypeptide and to the DNA encoding this polypeptide. The invention further relates to methods for preparing variants of this beta integrin subunit.
2. Description of Background and Related Art
The integrins are a family of plasma-membrane bound cell surface proteins. Many integrins exist; some are cell-type specific while others are present in several types of cells. At least one integrin has been found in nearly every animal cell type that has been evaluated (Hemler, Ann. Rev. Immunol., 8:365 [1990]; Albelda et al., FASEB J., 4:2868 [1990]) suggesting they may be ubiquitous in the animal kingdom.
Each integrin consists of an alpha polypeptide subunit and a beta polypeptide subunit. The subunits are non-covalently bound in such a way as to confer ligand-binding activity on the complex as a whole. Both types of subunits have three domains: 1) a cytoplasmic domain, which is the carboxyl terminus of the polypeptide, 2) a membrane-spanning or transmembrane domain, which is located near the carboxyl terminus and serves to anchor the polypeptide into the plasma membrane, and 3) an extracellular domain which binds ligand.
Several alpha subunits are known, (see Ruoslahti, J. Clin. Invest., 87:1 [1991]), and three human beta subunits have been known for some time. Recently, three additional human beta subunits have been identified, cloned and sequenced, and named beta-4 (Suzuki et al., EMBO J., 9:757 [1990]; Hogervorst et al., EMBO J., 9:765 [1990]), beta-5 (McLean et al., J. Biol. Chem., 265:17126 [1990]; (Ramaswarmy et al., EMBO J., 9:1561 [1990]) and beta-6 (Sheppard et al., 265:11502[1990]). A seventh beta subunit, beta-7, has just been reported (Yuan et al., Internat'l. Immunol., 2:1097 [1990]. Alpha and beta subunits can associate with each other in a variety of combinations thus creating a large number of distinct integrins (see Albelda et al., supra and Helmer, supra).
The human beta integrin subunits that have been identified to date share an amino acid sequence identity of around 32-56 percent and show conservation of about 50 cysteine residues (Yuan et al., supra). The beta-1 integrin subunit has an 82-90 percent homology between human, chicken, frog, and mouse (Hemler, supra), suggesting a highly conserved functional role for this subunit.
The integrins are known to mediate cell adhesion. One of the ways this mediation can occur is via the integrin binding to the extracellular matrix. Certain integrins have been shown to bind to such extracellular matrix proteins as fibronectin, fibrin, laminin, some collagens, tenascin, vitronectin, and von Willebrand factor (Ruoslahti, supra). A second way in which integrins can mediate cell adhesion is through cell-cell binding. For example, one integrin glycoprotein, Ilb/Illa, located on the surface of platelets, promotes the binding of platelets to each other via mediator molecules, especially fibrinogen. Other integrins have been shown to have a role in mediating the attachment of circulating leukocytes to tissue, thus removing them from circulation, which is important in tissue repair (Ruoslahti, supra).
It has been observed that the extracellular matrix surrounding many tumorigenic cells is less extensive than that observed for normal, non-tumorigenic cells, leading to enhanced mobility of tumor cells as compared to normal cells (Ruoslahti, supra). It has been shown that the integrin alpha-5/beta-1, as well as certain other integrins, have an altered level of expression in certain tumor cells (Plantefaber et al., Cell, 56:281 [1989]).
Recent research has suggested that some integrins may have a role in mediating the movement of neurons along glial fibers during development and differentiation of the cerebellum (Hatten, Trends. Neurol Sci., 13:179[1990]; Sanes, Ann. Rev. Neurosci., 12:491 [1989]).
There is a current and continuing need in the art to identify new integrin subunits and to identify their biological role(s), including their roles in mediating cell-cell adhesion, cell mobility, and cell adhesion to the extracellular matrix.
Accordingly, it is an object of this invention to identify a novel beta subunit integrin polypeptide that shares some common structural features with beta integrin subunits 1-7.
It is another object to provide nucleic acid encoding the novel beta integrin subunit polypeptide and to use this nucleic acid to produce the polypeptide in recombinant cell culture for research or diagnostic use, or for potential therapeutic use in certain neurological or immunological disorders and with certain tumors and tumorigenic cells.
It is a further object to provide derivatives and modified forms of the novel beta integrin subunit, including amino acid sequence variants and covalent derivatives thereof.
It is an additional object to prepare immunogens for raising antibodies against the novel beta integrin subunit, as well as to obtain antibodies capable of binding to the beta integrin subunit. It is a further object to prepare immunogens for raising antibodies against a complex comprising a novel beta integrin subunit which is associated with an alpha integrin subunit. It is preferable that the antibodies raised against these novel immunogens will not bind to beta integrin subunits 1-7.
These and other objects of the invention will be apparent to the ordinary artisan upon consideration of the specification as a whole.